In recent years, optical sheets that have fine texture patterns on their surfaces and offer intended functions with this textured structure refracting light have become indispensable for displays such as liquid crystal display devices, and these optical sheets are required to have various properties such as high refractive indices and a shape retaining property. Examples of the optical sheets include Fresnel lens sheets and lenticular sheets used in projection screens of projection televisions etc., prism sheets and microlens sheets used as backlights of liquid crystal display devices etc., and moth-eye films which have recently drawn attention as the antireflection films for flat-screen televisions.
These optical sheets, for example, a prism sheet (optical sheet) used for a backlight of a liquid crystal display device or the like, is formed by using a resin material, and this resin material is required to have performance and properties at high levels. For example, the resin material must be in a liquid state, must be of a solvent-free type so that the production process does not need a solvent drying time, must have a low viscosity suitable for coating despite being of a solvent-free type, and must have a high refractive index so as to maintain luminance at a small quantity of light.
As such a material having a high refractive index, a urethane acrylate having high aromaticity obtained by reacting bisphenol F diethoxy glycol, tolylene diisocyanate, and 2-hydroxyethyl acrylate in the molecular structure is known, and a technique of producing an optical sheet by using this urethane acrylate as a main component is known (for example, refer to PTL 1).
However, although the optical sheet described in PTL 1 achieves a high refractive index of 1.55 or more due to the highly aromatic resin material, the optical sheet does not currently satisfy the high refractive index property recently required for lens sheets to achieve ever higher luminance. Attempts have been made to use isocyanate compounds having higher aromaticity, for example, diphenylmethane diisocyanate, in order to achieve an ever higher refractive index; however, in this case, the resin material exhibits high viscosity and becomes crystalline, which makes forming into optical components difficult.